Rhodium-catalyzed synthesis of 1-alkynylphosphine oxides from 1-alkynes and tetraphenylbiphosphine

Article abstract of DOI:10.1016/j.tetlet.2006.04.158

A rhodium complex RhH(PPh₃)₄ catalyzes the C-P bond forming reaction of 1-alkynes and tetraphenylbiphosphine in the presence of 2,4-dimethylnitrobenzene giving 1-alkynylphosphines and its oxides.

Full text of DOI:10.1016/j.tetlet.2006.04.158

Tetrahedron Letters 47 (2006) 5211–5213
Rhodium-catalyzed synthesis of 1-alkynylphosphine oxides from
1-alkynes and tetraphenylbiphosphine
Mieko Arisawa, Masato Onoda, Chieko Hori and Masahiko Yamaguchi*
Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
Received 27 March 2006; revised 28 April 2006; accepted 28 April 2006
Available online 5 June 2006
Abstract—A rhodium complex RhH(PPh3)4 catalyzes the C–P bond forming reaction of 1-alkynes and tetraphenylbiphosphine in
the presence of 2,4-dimethylnitrobenzene giving 1-alkynylphosphines and its oxides.
Ó 2006 Elsevier Ltd. All rights reserved.
Previously, we reported the C–S bond forming reaction
of 1-alkynes and dialkyl disulfides in the presence of
RhH(PPh3)4 giving alkylthioacetylenes,1 a metathesis
reaction of the S–S and C–H bond. It was also found
that the same rhodium complex catalyzed the metathesis
reaction of biphosphine disulfides (dioxides) and dialkyl
disulfides giving dithiophosphinates, in which the S–S
and P–P bond exchange took place.2 It was therefore
considered that C–P bond could be formed by the bond
metathesis of P–P and C–H, and described here is the
rhodium-catalyzed synthesis of 1-alkynylphosphines
and its oxides from 1-alkynes and tetraphenylbiphos-
phine in the presence of 2,4-dimethylnitrobenzene.
Reported syntheses of 1-alkynylphosphines from 1-alky-
nes and phosphine chloride in general employed stoichio-
metric amounts of organometallic bases of lithium or
magnesium.3 The reaction using a stoichiometric tita-
nium tetrachloride and triethylamine was reported.4
Beletskaya developed nickel or copper catalyzed reac-
tions in the presence of triethylamine.5 In some cases,
organic bases such as triethylamine or iminophosphines
were used for such C–P bond formation.6 In contrast,
the present reaction employs a rhodium catalyst in the
absence of any added base but in the presence of a nitro-
benzene, which plays several critical roles in the
reaction.
oxide 3 and 1-dodecynyldiphenylphosphine 4 were ob-
tained in 74% and 6% yield, respectively (Table 1, entry
6). A considerable part of 6 was converted to a phosphi-
nic amide 5 in 56% isolated yield. The rhodium complex
was essential, and no reaction took place in its absence.
The nitrobenzene 6 was also required, and, in the ab-
sence, (E)-1-dodecenylphosphine oxide 77 was formed
in 32% yield with no traces of 3 and 4 (entry 1). The
Table 1. Effect of nitrobenzene in the C–P bond formation reaction of
1 and 2
O
RhH(PPh3)4 (9 mol%)
toluene, refl., 5 h
n-C10H21
+
H 1
3
n-C10H21
n-C10H21
PPh2
+
+
Ph2P PPh2
2
4
PPh2
+
ArNO2
ArNHPOPh2
5
Entry
Ar
Yield (%)
3
4
1
2
3
4
5
6
7
8
9
None
C6H5
0a
57
57
74
73
74
68
58
46
0
10
13
Trace
0
6
16
0
17
p-MeC6H4
m-MeC6H4
o-MeC6H4
2,4-Me2C6H3
2,3,4,5-Me4C6H
p-NCC6H4
When 1-dodecyne 1 was treated with tetraphenylbiphos-
6
phine
2 (2 equiv) and 2,4-dimethylnitrobenzene 6
(2 equiv) in the presence of RhH(PPh3)4 (9 mol %) in
refluxing toluene for 5 h, 1-dodecynyldiphenylphosphine
p-MeOC6H4
a
n-C10H21
Alkene 7 was formed in 32% yield.
*
Corresponding author. Tel.: +81 22 795 6812; fax: +81 22 795
6811; e-mail: yama@mail.pharm.tohoku.ac.jp
POPh2
7
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.04.158

5212
M. Arisawa et al. / Tetrahedron Letters 47 (2006) 5211–5213
Table 2. Rhodium-catalyzed synthesis of 1-alkynylphosphine oxides
from 1-alkynes
O
Ph2P PPh2
+
2
8
Ph2P PPh2
6
+
R
H
toluene, refl., 1 h
Me
NO2
H2O2
O
PPh2
+
RhH(PPh3)4
Me
N
PPh2
R
Me
6
toluene, refl., 5 h
Ph2P PPh2
2
POPh2
9
Me
Entry
R
Yield (%)
Scheme 1.
1
2
3
4
5
6
7
8
9
n-C8H17
n-C10H21
Ph(CH2)2
MeO(CH2)9
BnO(CH2)9
t-BuCOO(CH2)9
n-C4H9CH(C2H5)
1-Adamantyl
p-CH3C6H4
84
80
78
70
84
83
83
54
35a
ratio by 31P NMR, the latter of which was isolated in
16% yield (Scheme 1). This oxidation–reduction reaction
did not require the rhodium complex. Notably, both 8
and 9 were involved in the C–P bond formation reaction
of 1. The treatment of 1 and 8 (2 equiv) in the presence
of RhH(PPh3)4 (9 mol %) and 6 (2 equiv) in refluxing
toluene for 5 h gave 3 in 69% yield, where 4 was not
detected (Scheme 2). The rhodium complex and 6 were
essential for this reaction. When 9 was reacted with 1
in refluxing toluene for 5 h in the presence of the
rhodium complex (9 mol %), 4 (39%) and 3 (13%) were
obtained (Scheme 3). The rhodium complex was
confirmed to be essential for this reaction. The role of
6 therefore was to activate 2 giving either 8 or 9, both
of which reacted with 1 to form the C–P bond.
a The reaction was conducted at 100 °C for 1 h. (E)-2-(p-Tolyl)eth-
enyldiphenylphosphine oxide was also formed in 38% yield.
structure of the nitrobenzene had some effect on the
reaction: use of polymethylated nitrobenzenes gave
higher yields of 3 and 4 compared to nitrobenzene and
p-cyanonitrobenzene (entries 2–8); use of 2,3,4,5-tetra-
methylnitrobenzene and p-(methoxy)nitrobenzene in-
creased the amount of 4 (entries 7 and 9).
The experiments also revealed the presence of two inde-
pendent processes in the present C–P bond formation
(Scheme 4): the phosphine oxide 3 was formed from
biphosphine monoxide 8; the phosphine 4 from 9. The
oxidation of 4 to 3 was unimportant; the treatment of
4 and 6 in refluxing toluene for 2 h gave a very small
amount of 3, which indicated that the oxidation of 4
to 3 was much slower than that of 2 to 8. The rhodium
complex probably activated 9 by the chelate formation
between the O and P atoms. Analogous S and P chelat-
ing transition metal complexes were reported,10 and 9 is
now shown to function as a novel phosphinylating
reagent.
Several aliphatic 1-alkynes were reacted with 2 (2 equiv)
in the presence of 6 (2 equiv) and RhH(PPh3)4 (9 mol %)
giving ca. 1:10 mixtures of 1-alkynylphosphines and its
oxides, which were treated with 30% H2O2 to convert
the small amounts of the phosphines to the oxides (Ta-
ble 2).8 The reaction of aromatic 1-alkynes was less effi-
cient; the treatment of p-tolylacetylene and 2 in toluene
at 100 °C for 1 h followed by H2O2 gave (p-tolyleth-
ynyl)phosphine oxide (35%) and (E)-(p-tolyl)ethenyl-
diphenylphosphine oxide (38%).
The role of the nitrobenzene is intriguing. As apparent
from the formation of phosphinic amide 5, 6 trapped
Ph2PH, which should formally be formed from 1 and
2. In addition, 6 was involved in several critical steps
in the reaction. When 2 and 6 were reacted in refluxing
toluene for 1 h, 2 disappeared with the formation of
biphosphine monooxide 8 and an adduct 99 in a 4.5:1
In summary, rhodium-catalyzed C–H and P–P bond
metathesis reaction of 1-alkynes and biphosphine giving
1-alkynylphosphine oxide was developed, and a nitro-
benzene was found effectively to activate the P–P bond
for the transition metal catalysis.
6 (2 eq)
1
n-C10H21
H
O
RhH(PPh3)4 (9 mol%)
+
n-C10H21
PPh2
O
toluene, refl., 5 h
8 (2 eq)
3
69%
Ph2P PPh2
Scheme 2.
n-C10H21
H
1
RhH(PPh3)4 (9 mol%)
toluene, refl., 5 h
+
39%
13%
n-C10H21
PPh2
4
3
PPh2
+
O
PPh2
Me
N
n-C10H21
POPh2
Me
9
Scheme 3.

M. Arisawa et al. / Tetrahedron Letters 47 (2006) 5211–5213
5213
PPh2
1
Me
N
n-C10H21
PPh2
RhH(PPh3)4
POPh2
4
Me
9
Ph2P PPh2
2
+
Me
NO2
Me
O
O
1 + 6
6
Ph2P PPh2
n-C10H21
PPh2
RhH(PPh3)4
3
8
Scheme 4.
7. The oxygen atom on 7 may be derived from a small
amount of oxygen contaminated.
Acknowledgments
8. In a two-necked flask equipped with a reflux condenser
were placed 2 (0.25 mmol, 93 mg), 6 (0.25 mmol, 33.8 lL),
and RhH(PPh3)4 (9 mol %, 13 mg) under an argon atmo-
sphere. Degassed toluene (1 mL) and 1 (0.125 mmol,
27 lL) were added, and the solution was heated at reflux
for 5 h. Then, 30% hydrogen peroxide (0.25 mL) in THF
(5 mL) was added to the solution at 0 °C, and the mixture
was stirred for 1 h at the temperature. Aqueous sodium
thiosulfate was added, and the organic materials were
extracted with ethyl acetate. The organic layer was washed
with water and brine, dried over MgSO4, and filtered.
After removal of the solvents, flash chromatography
(hexane/ethyl acetate = 2/1) over neutral silica gel gave 3
(36.7 mg, 80%) as pale yellow oil.
M.A. expresses her thanks to the Grant-in-Aid for Sci-
entific Research on Priority Areas, ‘Advanced Molecu-
lar Transformation of Carbon Resources’ from MEXT
(No. 18037005). This work was supported also by JSPS
(Nos. 16109001 and 17689001).
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